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AS A SAMPLING METHOD
There are a number of ways to collect fish for management and research, and there are various methods involving traps and nets to capture different types of fish and each method has its own advantages and shortcomings. The technique of electrofishing is perhaps one of the most useful and effective for projects that require the collection of a relatively large number of fish. Electrofishing involves the use of DC current conducted through water to stun fish for collection. It may be utilized in most aquatic environments. There are two primary adaptations of this technique: backpack electrofishing, and boat electrofishing.
Backpack electrofishing is most commonly employed in streams or shallow waters that allow one to walk through the water wearing chest waders.
The person using the backpack unit carries two poles (usually tubular fiberglass). Each pole has an electrode on the end, one a cathode and one an anode. Insulated wires connect the electrodes to the backpack unit. The backpack unit itself is housed in waterproof casing and mounted on a non-conductive frame. Power is supplied from a battery, conventionally 12-24V DC. Outputs from back mounted units can range anywhere from 100V to over 1000V DC with amperage from 10-60A. Maximum output power also varies from about 8Kw-70Kw. All backpack units offer the ability to select different levels of output and some of the more costly models offer different waveform selection to maximize the efficiency of battery use. Some models may last only a couple of hours at a medial output while others incorporate secondary batteries to provide longer periods of use. Using high-energy pulses of electricity is often preferred to a constant level of output, although intense pulses may be harmful to smaller fishes. Backpack electrofishing units can be somewhat costly; lower end models having only basic features are priced around $1500. The more elaborate models can cost in excess of $2000.
When using backpack electrofishing units in an environment such as a small stream, there are several conventions that may be followed to enhance the productivity of the technique. Site selection is the perhaps the most important factor. If a representative sample is taken, one must choose small areas which are representative of the different types of habitats common to the stream. Comparative samples should be chosen so that each sample will represent one of the types of habitats found in the stream. One common convention is to set up block nets upstream and downstream from the sampling site. If accomplished inconspicuously, it can prevent fish from leaving the site when disturbed by people who are wading. Once the block nets are set, walking through the site can cause the fish to move from feeding or refuge sites. Backpack electrofishing is most effective when there is more than one person carrying shocking units. Shockers should make a systematic sweep of the site area while other researchers follow along and collect the stunned fish with dip nets. Sequential passes should be performed identically to the first one. Always record the area and length of time of the sample.
Electrofishing boats are most useful in lakes or rivers where the area to be sampled is much greater. In this technique, flat bottom boats are equipped with booms that extend usually over the bow of the craft. The booms can be equipped with multiple electrodes that may be set at varying depths and therefore sample a larger area. On an electrofishing boat, it is most efficient to supply power from an on board generator. The AC current produced will then be converted to a pulsed DC current. Boat electrofishing systems are much more expensive than the backpack units. Most suppliers offer systems starting around $5,000 and ranging up to $15,000.
When collecting samples using this technique, it is best to have two or three people on board. One must drive the boat; others collect the fish and manage the equipment. Collected specimens should be kept in a live well until they have served their purpose. Choosing a depth and place to sample is an important factor in this technique also. Due to the fact that fish cannot be isolated as they are in streams, the sample will be more random. If
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